On the day he died, Jimi Hendrix was at the peak of his career--and deep in debt.

The 27-year-old rocker was one of the most successful artists of the '60s psychedelic era. He had recorded five top-selling albums and was one of the highest-paid concert performers of his day ($125,000 per show). But he owed tens of thousands of dollars to his record company and was the target of numerous lawsuits, ranging from management contract disputes to a paternity suit.

After his death, a series of bad investments and bitter litigation battles nearly drove his estate into bankruptcy.

But in the last decade, the Hendrix legacy has witnessed a dramatic turnaround. Twenty years after his demise, the acclaimed guitarist actually makes more money dead than he did alive.

Unlike other prominent figures of the psychedelic generation, Hendrix has little difficulty competing in today's video-heavy, high-tech market. Only three other deceased stars in the history of rock--Elvis Presley, John Lennon and Jim Morrison--rival his marketability.

The combination of record sales, the merchandising of Hendrix's likeness and song publishing is a multimillion-dollar enterprise--though the exact figures are tightly guarded. In 1988, Forbes magazine estimated the gross annual income from the guitarist's music publishing and record royalties at $4 million, but the guardians of his fortune dismiss the figure as "an inaccurate guess."

Those promoting the Hendrix legacy predict that he will sell between 2 and 3 million records internationally this year. Merchandisers estimate that they will sell more than $1 million worth of garments, posters and paraphernalia bearing his name and likeness in 1990. Ten books about his life are also being prepared for publication--and that's just the tip of the iceberg.

In commemoration of the 20th anniversary of his passing on Sept. 18, 1970, the National Film Theatre in London is scheduled to premiere a film Tuesday of Hendrix's last major concert at the Isle of Wight Festival.

In November, Warner Bros. Records will release "Lifelines," a biographical four-CD set featuring interviews, studio outtakes and home demo and concert tapes culled from a 1988 Westwood One radio show. The collection also includes a previously unreleased concert recording from a 1970 show at the Forum in Inglewood.

Alan Douglas, who owns and operates Are You Experienced?, Ltd., the Hollywood-based company in charge of merchandising official Hendrix music and memorabilia, insists the appetite for Hendrix material these days is insatiable.

"Hendrix is going on his third generation of fans," Douglas said. "Nobody has to update or manufacture some aura of mystique to sell Jimi. All we have to do is release new evidence of his greatness every once in a while. The music speaks for itself."

Douglas, who first worked with Hendrix in 1969 and was hired by his estate to produce posthumous releases in 1974, estimates that 75% of Hendrix's current audience is between 12 and 20 years of age. The 59-year-old producer thinks the reason Hendrix's music holds up is because the rock star was so far ahead of his time.

"He's still the reference point by which great artists judge relevant electric guitar music," Douglas said. "No instrumentalist has yet to create anything which makes his contribution sound obsolete."

Hendrix's original five Reprise albums have all surpassed the 3-million mark, and sales are on the rise. According to Bob Merlis, vice president of national publicity at Warner Bros., the Hendrix catalogue currently generates sales of between 500,000 and 1 million copies a year.

"Item for item," Merlis said, "Jimi Hendrix's catalogue is probably the strongest in the business."

Three years ago, Los Angeles-based Rykodisc released a super-clean CD remix of an October, 1968 concert titled "Live at Winterland," which sold 200,000 copies in 1987. The sound quality of the Rykodisc recording and the corresponding consumer response inspired Warner Bros. to reissue nine digitally remastered Hendrix albums last year.

The collection includes "Smash Hits," a best-of compilation first released in 1969 containing such classics as "Foxy Lady" and " Purple Haze." It comes with a new high-tech graphics track that allows fans who own a JVC CD-plus-graphics unit to view synchronized psychedelic imagery while listening.

PolyGram Records, the company responsible for distributing Hendrix's music overseas, has plans to release an updated series of Hendrix reissues, employing a new mastering technique developed by engineer Joe Gastwert that reportedly will improve the CD sound quality.

"Lifelines," the upcoming four-CD box set on Warner Bros., is but the first in a series of annual box sets Are You Experienced?, Ltd., intends to deliver. Douglas' engineering crew is currently wading through hundreds of hours of unreleased club and concert master recordings for future compilations.